Signal detection

ABSTRACT

A method, apparatus, and system for detecting a signal of interest. According to some embodiments, a power of a frequency component of a signal is determined. The power is accumulated for a first period and a second period, the second period being shorter than the first period. Power spectrum information may be found, and high and normalized power spectrum information may be determined and compared.

This application is a continuation of prior U.S. patent application Ser.No. 10/662,600 entitled “Signal Detection” and filed Sep. 15, 2003. nowU.S. Pat. No. 6,941,237

BACKGROUND

Public Switched Telephone Network (PSTN) alerting signals, includingCall-Waiting and Caller-ID alerting signals, are communicated usingnumerous standards throughout the world. Typically, modems are manuallyconfigured through a homologation process so that they will operateutilizing a desired standard. Most countries, and even portions ofcountries, use different standard, however, such that there may behundreds of standards being utilized throughout the world at any giventime. Thus, manual configuration may be time consuming. Furthermore,such manual configuration is generally difficult, such thatconfigurations defined for certain standards may not work reliable.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, wherein like reference numerals are employedto designate like components, are included to provide a furtherunderstanding of signal detection, are incorporated in and constitute apart of this specification, and illustrate embodiments of signaldetection that together with the description serve to explain theprinciples of signal detection.

In the drawings:

FIG. 1 illustrates an embodiment of a signal receiving device;

FIG. 2 illustrates an embodiment of a method of detecting a signal;

FIG. 3 illustrates an embodiment of a device suitable for detecting asignal;

FIG. 4 is a block diagram of an embodiment of a telephony network inwhich a signal may be detected.

DETAILED DESCRIPTION

Systems, apparatuses, and methods for automatically detecting signals,including PSTN alerting signals, are provided. Those signals may beaudio frequency signals and those audio signals may be sampled at asampling rate which may be in the range, for example, of 7200 to 10286Hz. Those signals may include information unrelated to the signalsdetected by the systems, apparatuses and methods described herein.Information may comprise any data capable of being represented as asignal, such as an electrical signal, optical signal, acoustical signaland so forth. Examples of information in this context may include analogor digital voice communications, images, video, text, data and so forth.

As is known to those skilled in the area of frequency sampling, and asstated by the Nyquist Theorem, an important consideration for samplingis that the sampling rate must be at least twice the highest analogfrequency component of a portion of a signal being sampled that isdesired to be measured. The Nyquist Theorem suggests that for a digitalrepresentation of an analog signal, such as an audio signal, toaccurately represent the analog signal, the sampling rate must be atleast twice the highest analog frequency component of interest in thatsignal.

The number of samples to be taken into consideration for a powerspectrum tap may include at least one complete wave (360 degrees) of thesignal being sampled. In such a situation where at least one wave, suchas a sine wave that is regularly repeating on the signal, is desired ina power spectrum tap, enough samples of the signal will be taken toassure that those samples cover a range of the signal that shouldinclude at least one complete wave of the signal. For example, foursamples may describe a complete sine wave in a particular signal wherethe sampling rate is twice the highest frequency component of thesignal.

A number of samples to be taken may, for example, be calculated bydividing a chosen sampling rate, which may be measured in samples persecond, by the lowest frequency of interest, generally measured in Hertz(Hz). Thus, for example, if the sampling rate chosen is 2400 samples persecond and the lowest frequency of interest is 100 Hz, then the numberof samples that could be taken at one time for Fourier analysis might be2400/100, or 24 samples.

Additional samples may be included to improve accuracy of the powerspectrum measured. A maximum number of taps to be included in a powerspectrum may be limited by an amount of memory or processor timeavailable for processing the power spectrum taps. A number of samplesmay thus be selected practically to provide enough accuracy to identifya standard from amongst multiple standards on which the signal is beingcarried.

Initially, a power spectrum may be generated from the appropriate numberof samples of an analog stream representing or carrying the signal to beexamined. Then a difference between an average frequency of that powerspectrum and a peak frequency for a portion of that power spectrum maybe determined. A Fourier transform may, for example, be utilized toprocess audio sample blocks of the signal as is known in the signalprocessing technologies. The sampling system may sample those blocks ofthe audio carrying signal at discrete intervals. The Fourier transformmay then convert the sampled signal to a function of frequency. Thatfrequency, in turn, may reveal the signal, which may be carried on asingle frequency or may be carried over a set of frequencies known as a“carrier set.” The multiple signals carried may in turn be referred toas “multi-tone.”

A carrier set is one or more frequencies capable of being modified tocarry information by, for example, amplitude modulation, frequencymodulation, or phase modulation. Amplitude is the signal strength, orsignal power, and is the relative “height” of the wave. Frequency is therate at which an electromagnetic waveform alternates as is usuallymeasured in Hertz (cycles per second) and equals the number of completecycles occurring in one second. Phase is the relationship between asignal and its horizontal axis, also called the zero access point. Afull signal cycle describes a 360° arc. Embodiments of standarddetection could be used in frequency modulation and other modulationbased techniques.

The carrier set in DSL, for example, allows 1 bit stream to be carriedon a multi-tone signal. Carrier set A43, for example, specifies threedownstream frequencies of 40 times 4.3125 kHz, 56 times 4.3125 kHz, and64 times 4.3125 kHz creating a multi-tone signal. Those tones combine tosend a signal. Information, typically in the form of bits of data, aretransmitted by changing some feature of the signal (e.g., frequency,amplitude or phase of the signal), transmitting the signals bymodulation from the transmitting node, and then changing the signal backby demodulation upon reception at the receiving node. Of course, similarcarrier systems allow for multiple information channels to be carried bymany other broadband systems as well.

A43, B43, and C43 carrier sets are used principally with AsymmetricDigital Subscriber Lines (ADSL) in different parts of the world, withA43 used primarily in North America, B43 used primarily in Europe, andC43 used primarily in Japan. An A4 carrier set is a member of the 4 kHzsignaling family that uses a single upstream carrier frequency andsingle downstream carrier frequency. The A4 carrier set is usedprimarily with Symmetric Digital Subscriber Line (DSL) modem types.

To generate the power spectrum, magnitude and phase of a sample of thesignal, corresponding to the desired power spectrum, may be calculated.The magnitude of the power spectrum may be calculated, for example, byperforming a real portion of a Discrete Fourier Transform (DFT) or aFast Fourier Transform (FFT), and the phase of the power spectrum may becalculated by performing an imaginary portion of the DFT or FFT.

The device performing the Fourier transform may be any device programmedor created to perform the Fourier transform. For example, the device maybe a processor such as a digital signal processor (DSP). The DSP oranother device may seek a detector threshold that is greater than afrequency at which no audio component is present on the signal and lessthan a frequency at which one or more audio components are indicated onthe signal. By using the detector threshold, a signal level indicatingthat the desired component is present on the signal may be distinguishedand detected. Thus, utilizing that detector threshold, the DSP maydetermine whether a frequency on the sampled signal is greater than thethreshold, indicating that at least one audio component is present onthe signal.

A frequency component of the power spectrum, having one or moreamplitudes, may then be created by applying the Pythagorean Theorem tothe magnitude and phase of the sample. In doing so, the two portions ofthe Fourier Transform are squared, added together, and then the squareroot of that sum is taken. The result may be viewed as one frequencycomponent of the power spectrum of the signal.

A power spectrum may be viewed as a signal relative to frequencytransformed from a signal relative to time. In other words, the powerspectrum separates the signal into various frequency components thateach include a range of frequencies. Each range of frequencies mayfurthermore have one or more amplitudes associated therewith, thoseamplitudes corresponding to power in that frequency range. A tap maythen be the amount of power that the signal contains within a frequencyrange corresponding to one of those frequency components.

Multiple most recent power taps may be taken and integrated over timeby, for example, an infinite impulse response (IIR) filter or otherdigital signal filter to create a long-term integrated power spectrum.An IIR filter generally outputs a weighted sum of its inputs withgreatest weight placed on most recent input samples and lesser weightplaced on older samples. For example, a long-term integrated powerspectrum may be calculated utilizing a set of IIR filters, one per tap,each one with a time constant of 400 milliseconds (mS), a time periodthat may be suitable to represent a long-term integrated power spectrum.

The term “time constant” may be defined as the time required for theamplitude of a signal to rise or fall exponentially by approximately 63%of its peak or trough. A time constant of 400 mS thus may roughlyindicate that the effect of a particular sample is reduced byapproximately 37% of its original value after 400 mS. It generally takesabout 2.3 time constants for the effect of a particular sample to dropto 10% of its original value. Thus, a higher time constant will resultin a slower response to changing input values and a lower time constantwill result in a faster response.

The most recent power taps may similarly be integrated over time togenerate a short-term integrated power spectrum. For example, ashort-term integrated power spectrum with a time constant of 200 mS maybe appropriate.

The long-term integrated power spectrum may then be subtracted from theshort-term integrated power spectrum to generate a delta integratedpower spectrum. Thus the delta integrated power spectrum may represent ashort-term deviation from a long-term power level experienced for thesensed frequency range.

A plurality of delta integrated power spectrum values may be calculatedand added together in, for example, an accumulator device or a variable.Once the delta integrated power spectrum has been accumulated for adesired period of time, a complete delta power spectrum has beengenerated. The complete delta power spectrum may then be divided by thenumber of delta integrated power spectrum values include therein to findan average power in the complete delta power spectrum. The number ofdelta integrated power spectrum values that are accumulated in thecomplete delta power spectrum may vary as desired. Accumulation of 48delta integrated power spectrum values has been found to be sufficient,while more delta integrated power spectrum values may be accumulated toincrease accuracy and fewer delta integrated power spectrum values maybe accumulated to reduce processing and overhead.

A plurality of individual delta integrated power spectrum values mayfurthermore be retained. For example, six delta integrated powerspectrum values may be retained in a priority queue. The value of eachnew delta integrated power spectrum may be compared to the values in thepriority queue and a new delta integrated power spectrum value mayreplace the lowest value in the priority queue if the new deltaintegrated power spectrum value is greater than that lowest value.

A standard utilized for the signal may then be determined from themeasurements taken once one or more complete delta power spectrums hasbeen generated. To determine the standard, the average of the deltaintegrated power spectrums in a complete power spectrum may becalculated. Simultaneously, if desired, the most powerful deltaintegrated power spectrum values for the completed delta power spectrummay be moved from the priority queue to another memory location so thatdelta integrated power spectrum values from another delta integratedpower spectrum may be stored in the priority queue. Thus, a new completedelta power spectrum may be created while calculations for a pastcomplete delta power spectrum are simultaneously computed. Those mostpowerful delta integrated power spectrum values moved from the priorityqueue may then be sorted by frequency.

Delta integrated power spectrum values that were taken at adjacent timesmay then be combined. Adjacent delta integrated power spectrum valuesmay be combined by adding their powers and frequency ranges andreplacing the two adjacent delta integrated power spectrum values with asingle combined delta integrated power spectrum value. Combination ofadjacent delta integrated power spectrum values may be performed becausewhen using a DFT, if an input frequency is the frequency of a particulardelta integrated power spectrum, the full power of the delta integratedpower spectrum will be recorded as desired. If, however, the tone orother portion of the signal to be detected falls between two deltaintegrated power spectrums, then its power will be will be recorded asbeing distributed between those two delta integrated power spectrums.Thus, by combining the neighboring delta integrated power spectrums,accurate power and frequency values may be obtained for the tone orother desired portion of the signal.

A significantly powerful delta integrated power spectrum is likely toindicate presence of a tone, while an insignificantly powerful deltaintegrated power spectrum is likely to indicate that no tone is present.Significance may be determined by subtracting the average deltaintegrated power spectrum value, calculated as described above, from thepower of the most powerful delta integrated power spectrum. Theresulting differential may then be compared to a high significancethreshold, which may be determined empirically so that tones aregenerally represented by powers above the high significance threshold.Thus, the most powerful delta integrated power spectrum value may bechosen and compared to the high significance threshold to determinewhether that delta integrated power spectrum value is significantlypowerful, thereby indicating the presence of a tone or other portion ofthe signal that is to be identified.

A time over which the most powerful tap is significant may then bedetermined. That significant time may begin when the power becomesgreater than the high significance threshold. That time may furthermoreend when the power becomes less than a low significance threshold. Thattime may further indicate whether a tone was present when the deltaintegrated power spectrum was taken, with a greater amount of timeindicating presence of the tone and a lesser amount of time indicatingno tone.

The use of a high and a low significance threshold may beneficiallyprovide hysteresis, which may avoid falsely detecting a start point of atone by avoiding signal anomalies caused by something other than a tonethat are higher than the low significance threshold, while continuing toregister tone signals until the low significance threshold is reached.

Thus, a minimum duration or time threshold, over which a tone should besignificant, may be compared to the time over which a tap is found to besignificant to further assure that the tap is experiencing a tone. Thatminimum time threshold may also be a predetermined amount of time andmay be determined empirically. The minimum threshold time may be set,for example, to half the length of time of the worlds shortest PSTNalerting signal where an alerting signal is desired to be sensed.

If the most powerful delta integrated power spectrum passes each ofthose tests: amount of power present and length of time present, it isassumed to be significant. Once significance has been assumed, values ofa number of most powerful delta integrated power spectrums from thecomplete power spectrum may be used, possibly along with the samplingfrequency, to determine which of a plurality of standards is beingutilized to carry the signal.

That information may further be reported to a host computer fordetermination of the applicable standard. A number of most powerfuldelta integrated power spectrum values to be reported that has been usedsuccessfully is the three most powerful delta integrated power spectrumvalues. The report may contain an amount of time that the signal wassignificant during the complete power spectrum, the frequency of thesignificant signal sensed at the most powerful delta integrated powerspectrums, a range of frequencies experienced during the most powerfuldelta integrated power spectrums, and the power of the most significantdelta integrated power spectrums. Moreover, if no delta integrated powerspectrum is found to be significant during a complete power spectrumthat may also be reported to indicate that information relating to thecarrier standard has not yet been sampled.

The information reported may then be compared to a variety of standardsand matched to the most closely conforming standard, which may beassumed to be the standard utilized with the signal.

FIG. 1 illustrates an embodiment of a signal receiving device 100. Thesignals received at the signal receiving device 100 may include PSTNalerting signals, which may be used to determine a standard by which thesignal is being transmitted.

An analog front end clock (“AFE clock”) 102 may be coupled to a signalat an input of the AFE clock 102 to transmit or receive datasynchronously across an analog medium. A down-sampler 104 may have aninput that is coupled to an output of the AFE clock 102 to sample asignal received from the AFE clock 102.

The down-sampler 104 generally creates a miniaturized duplicate of theoriginal signal, generally so that it can be processed or stored moreefficiently. Down-sampling allows the reduced signal to be used as aproxy, while preserving the information content of the original signal.A down-sampler 104 may, for example, decimate the proxy by retainingonly every other sample of the original signal. A down-sampler 104 mayalso act as a low-pass digital filter and may attenuate higher frequencysignals more than lower frequency filters. Such down-sampling may,however, cause the loss of some needed information contained in theoriginal signal. Thus, depending on the particular design requirements,a down-sampler 104 may combine decimation and a corrective filter tocompensate for the error that decimation alone would introduce. Usingdown-sampling, each output sample may be a function of two or more inputsamples.

A hum filter 106 may be used to remove hum from the signal and an echocanceller 108 may be used to remove echo from the signal. A gain control110 may be used to amplify the signal. The signal may then betransmitted from the gain control to a demodulator or interpolator 112and also to a signal detector such as the signal detector 114illustrated in FIG. 2. The sampling rate of the signal receiving device100 may also be transmitted to the signal detector.

FIG. 2 illustrates a signal detector 114. The signal detector 114 mayperform a discrete Fourier transform on the real portion of the signalat 116 and perform a discrete Fourier transform on the imaginary portionof the signal at 118. The magnitude of the signal resulting from theperforming the discrete Fourier transform on the real portion of thesignal is squared at 120 and the phase of the signal resulting from theperforming the discrete Fourier transform on the imaginary portion ofthe signal is squared at 122. The squared magnitude of 120 and thesquared phase of 122 are then added at 124 and the square root of thatsum is taken at 126 to provide one frequency component of the powerspectrum of the signal. That frequency component may include anamplitude having an amount of power referred to as a tap.

The frequency components are accumulated by an IIR over a long-term at128, resulting in a long-term integrated power spectrum and areaccumulated over a shorter term by an IIR at 130, resulting in ashort-term integrated power spectrum. A difference, referred to as adelta integrated power spectrum, between the long-term accumulation andthe short-term accumulation is calculated at 132.

A sum of a series of delta integrated power spectrums is accumulated at134 and divided by the number of delta integrated power spectrumsincluded in the sum to find an average delta integrated power spectrum.Alternately, the average delta integrated power spectrum may be anormalized power level experienced in a plurality of delta integratedpower spectrums. That average delta integrated power spectrum is used asa standard against which peak delta integrated power spectrums will becompared at 144 to determine their significance.

Simultaneously, if desired, the delta integrated power spectrums havingthe highest associated power values may be stored in a priority queue at136. The delta integrated power spectrums in the priority queue are thensorted by frequency at 138. Adjacent delta integrated power spectrumsare identified and combined as described herein at 140. The mostpowerful delta integrated power spectrum is then identified at 142.

At 144, the most powerful delta integrated power spectrum value iscompared to the average delta integrated power spectrum from 134. If themost powerful delta integrated power spectrum value is greater than theaverage delta integrated power spectrum by an amount in excess of anamplitude significance threshold, then that most powerful deltaintegrated power spectrum has passed an amplitude significance test.

If the most powerful delta integrated power spectrum has passed theamplitude significance test of 144, then that most powerful deltaintegrated power spectrum is put to a time interval significance test.If the power of the most powerful delta integrated power spectrum wasgreater than the amplitude significance threshold for more than aminimum duration, which may be established by setting a predeterminedtime threshold, then the most powerful delta integrated power spectrumpasses the time interval significance test at 146.

At 148, the sampling rate of the AFE hardware at 102 is determined andat 149, one or more of the most powerful delta integrated powerspectrums are compared to standards to determine to which standard theymost closely correspond. That determination may utilize the power andfrequency of the most powerful delta integrated power spectrums, and thesampling rate at which samples included in the delta integrated powerspectrums may be used in making that comparison. The sampling rate maybe used to calculate the actual frequency of the delta integrated powerspectrums for common comparison with the standards.

FIG. 3 illustrates an embodiment of a signal detector 150. The signaldetector 150 includes memory 152, a processor 154, a storage device 156,an output device 158, an input device 160, and a communication adaptor162. It should be recognized that any or all of the components 152–162of the signal detector 150 may be implemented in a single machine. Forexample, the memory 152 and processor 154 might be combined in a statemachine or other hardware based logic machine.

It should be recognized that the signal detector 150 may have fewercomponents or more components than shown in FIG. 3. For example, ifoutput devices 158 or input devices 160 are not desired, they may not beincluded with the signal detector 150.

The memory 152 may, for example, include random access memory (RAM),dynamic RAM, and/or read only memory (ROM) (e.g., programmable ROM,erasable programmable ROM, or electronically erasable programmable ROM)and may store computer program instructions and information. The memory152 may furthermore be partitioned into sections including an operatingsystem partition 166, wherein instructions may be stored, a datapartition 168 in which data may be stored, and a signal detectorpartition 170 in which instructions for identifying a standard utilizedin connection with a signal and stored information related to suchidentification may be stored. The signal detector partition 170 may alsoallow execution by the processor 154 of the instructions stored in thesignal detector partition 170. The data partition 118 may furthermorestore data to be used during the execution of the program instructionssuch as, for example, information related to standards to which theidentifying information is to be compared.

The processor 154 may execute the program instructions and process thedata stored in the memory 152. In one embodiment, the instructions arestored in memory 152 in a compressed and/or encrypted format. As usedherein the phrase, “executed by a processor” is intended to encompassinstructions stored in a compressed and/or encrypted format, as well asinstructions that may be compiled or installed by an installer beforebeing executed by the processor 154.

The storage device 156 may, for example, be a magnetic disk (e.g.,floppy disk and hard drive), optical disk (e.g., CD-ROM) or any otherdevice or signal that can store digital information. The communicationadaptor 162 may permit communication between the signal detector 150 andother devices or nodes coupled to the communication adaptor 162 at acommunication adaptor port 172. The communication adaptor 162 may be anetwork interface that transfers information from nodes 202–208 on anetwork such as the network 200 illustrated in FIG. 4, to the signaldetector 150 or from the signal detector 150 to nodes 202–208 on thenetwork 200. The network in which the signal detector 150 operates mayalternately be a Local Area Network (LAN), Wide Area Network (WAN), orthe Internet. It will be recognized that the signal detector 150 mayalternately or in addition be coupled directly to one or more otherdevices through one or more input/output adaptors (not shown).

The signal detector 150 may also be coupled to one or more outputdevices 158 such as, for example, a monitor or printer, and one or moreinput devices 160 such as, for example, a keyboard or mouse. It will berecognized, however, that the signal detector 150 does not necessarilyneed to have any or all of those output devices 158 or input devices 160to operate.

The elements 152, 154, 156, 158, 160, and 162 of the signal detector 150may communicate by way of one or more communication busses 164. Thosebusses 164 may include, for example, a system bus, a peripheralcomponent interface bus, and an industry standard architecture bus.

The network in which signal detection is implemented may be a network ofnodes such as telephones, computers, or other, typicallyprocessor-based, devices interconnected by one or more forms ofcommunication media. The communication media coupling those devices mayinclude, for example, twisted pair, co-axial cable, optical fibers andwireless communication methods such as use of radio frequencies. Networknodes may furthermore be equipped with the appropriate hardware,software or firmware necessary to communicate information in accordancewith one or more standards.

FIG. 4 illustrates an embodiment of a telephony network 200 in which twotelephony devices 202 and 204 are coupled to a PSTN 210 and twoadditional telephony devices 206 and 208 are coupled to a private branchexchange (PBX) 112 that is coupled to the PSTN 210 to form a telephonynetwork 200.

The PBX 212 is a telephone system, typically within an enterprise, thatswitches calls between telephony devices coupled to the PBX 212 andphone lines coupled to the PSTN 210. A typical PBX includes severalinterface circuits that are coupled to telephony devices and severalinterface circuits that are coupled to a PSTN. A switching portion ofthe PBX 212 makes connections between the telephony devices 206 and 208coupled to the PBX 212 and other telephony devices 202–208 coupled tothe PBX 212 or the PSTN 210.

The PSTN 210 may be a collection of telephony networks operated, for themost part, by telephone companies and administrative organizations.Signal detection may be performed in connection either with telephonydevices 202 and 204 coupled directly to a PSTN 210 or telephony devices206 and 208 coupled to a PBX 212.

Signal detection may be incorporated into a telephony device or may becoupled to a signal transmitting to a telephony device coupled to a PBX212 or PSTN 210. A signal detection device may thus take the form, forexample, of a node, such as a general purpose computer or applicationspecific circuit that couples to a signal being transmitted to or fromanother telephony device, or a telephony device such as a wireless orcordless telephone, two-way radio, or other telephone. A cordlesstelephone may include a telephone handset that communicates with aremote base station coupled to a PBX 212 or PSTN 210, for example, byway of signals carried by radio waves. Such cordless telephones mayinclude a radio-frequency transceiver and an omnidirectional antenna tocouple to the radio-frequency transceiver.

While the systems, apparatuses, and methods of signal detection havebeen described in detail and with reference to specific embodimentsthereof, it will be apparent to one skilled in the art that variouschanges and modifications can be made therein without departing from thespirit and scope thereof. Thus, it is intended that the modificationsand variations be covered provided they come within the scope of theappended claims and their equivalents.

1. A signal detection method, comprising: determining power of afrequency component of a signal; accumulating the power for a firstperiod; accumulating the power for a second period the second periodbeing shorter than the first period; determining power spectruminformation associated with a difference between the accumulated powerfor the first period and the accumulated power for the second period;finding high power spectrum information and normalized power spectruminformation; comparing the power of the high power spectrum informationto the power of the normalized power spectrum information; andoutputting a detection signal based at least in part on said comparing.2. The method of claim 1, wherein accumulating power includesintegrating the power using an infinite response filter.
 3. The methodof claim 1, wherein the first period is approximately 400 millisecondsand the second period is approximately 200 milliseconds.
 4. The methodof claim 1, further comprising: determining whether the high powerspectrum information represents a signal of interest, including: findinga power difference by subtracting the power of the normalized powerspectrum information from the power of the high power spectruminformation; and determining that the high power spectrum informationrepresents the signal of interest if the power difference exceeds apredetermined significance threshold.
 5. The method of claim 4, whereindetermining whether the high power spectrum information represents thesignal of interest further includes determining that the high powerspectrum information represents the signal of interest if the powerexceeds the significance threshold for at least a predeterminedduration.
 6. The method of claim 1, further comprising comparing thepower spectrum information to a plurality of standards to determine astandard to which the high power spectrum information most closelycorresponds.
 7. The method of claim 6, wherein multiple high powerspectrum are utilized in conjunction with a sampling rate at which thosehigh power spectrums were taken are used in the comparison.
 8. A signaldetection device, comprising: a processor to determine imaginary andreal portions of a signal and determine a frequency component of thesignal; a first filter to accumulate power of the frequency componentfor a first period; a second filter to accumulate power of the frequencycomponent for a second period, the second period being shorther than thefirst period; a first differentiator to calculate power spectruminformation associated with a difference between the accumulated powerfor the first period and the accumulated powwer for the second period; afilter to determine a normalized power for a plurality of powerspectrums; a memory to store a power valuer for a highest powerspectrum; and a second differentiator to determine whether the powervalue for the high power spectrum exceeds the normalized power for theplurality of power spectrums by at least a predetermined threshold. 9.The device of claim 8, wherein the imaginary and real portions of thesignal are determined by utilizing a discrete Fourier transform.
 10. Thedevice of claim 9, wherein determining the frequency component includesperforming the Pythagorean Theorem on the imaginary and real portions ofthe signals.
 11. The device of claim 8, wherein the first filter and thesecond filter are infinite impulse response filters.
 12. An article ofmanufacture, comprising; a computer readable medium having storedthereon instructions which, when executed by a processor, cause theprocessor to: determine power of a frequency component of a signal;accumulate the power for a first period; accumulate the power for asecond period, the second period being less than the first period; findpower spectrum information that is a difference between the accumulatedpower for the first period and the accumulated power for the secondperiod; select high power spectrum information; calculate normalizedpower spectrum information; compare the power of the high power spectruminformation to the power of the normalized power spectrum information;and output a detection signal based at least in part on said comparison.13. A modem, comprising: a demodulator to couple to an incoming signal;a processor to determine imaginary and real portions of a signal anddetermine a frequency component of the signal; a first filter toaccumulate power of the frequency component for a first period; a secondfilter to accumulate power of the frequency component for a secondperiod, the second period being shorter than the first period; a firstdifferentiator to calculate power spectrum information associated with adifference between the accumulated power for the first period and theaccumulated power for the second period; a filter to determine anormalized power spectrum information: a memory to store a power valuefor a highest power spectrum; and a second differentiator to determinewhether the stored power value exceeds the normalized power spectrumsinformation by at least a predetermined threshold.